Conveyor system with buffer arrangement

ABSTRACT

A conveyor system and the operation of a conveyor system will convey articles such as baggage at airports. A buffer arrangement is provided for storing and pre-sorting at least a part of the article-flow through the system. A conveyor system for conveying and sorting articles for a number of different destinations may be operated with a much lower number of stations for discharging the articles if the possibility of pre-sorting and temporarily storing the articles exists within the system. In particular, a storage rack can be provided for storing articles and the conveyor system comprising such a storage rack.

TECHNICAL FIELD

The present invention relates to a conveyor system and the operation ofa conveyor system for conveying articles, such as e.g. baggage at anairport, in which system a buffer arrangement is provided for storingand pre-sorting of at least a part of the article-flow through thesystem. A conveyor system for conveying and sorting articles for anumber of different destinations may be operated with a much lowernumber of stations for discharging the articles if the possibility ofpre-sorting and temporarily storing the articles exists within thesystem.

In particular, the invention concerns a storage rack for storingarticles and a conveyor system comprising such a storage rack.

BACKGROUND ART

A sorting and storage system for pieces of goods such as flight luggageis disclosed in U.S. Pat. No. 5,301,790, in which the luggage is placedon totes situated on a conveyor with tiltable carrying platforms. Theluggage may be conveyed directly to one of a number of destinationswhere it is unloaded from the tote, or it may be temporarily placed in astorage unit until a destination for that particular luggage is opened,whereupon the luggage is conveyed to that destination and unloaded fromthe tote.

Storage systems for storing early bags in a baggage handling system arealso disclosed in U.S. Pat. No. 5,413,205 and U.S. Pat. No. 5,575,375.These storage systems comprise a conveyor with multiple tray carriersarranged in a serpentine fashion for efficient use of horizontal space.Such storage systems are primarily used for storage of so-called earlybags for which the destinations are not opened yet.

DETAILED DESCRIPTION OF THE INVENTION

Conveyor systems for e.g. airports for conveying and sorting items, suchas luggage, for a number of different destinations need to have a highnumber of discharge stations for discharging items for specificdestinations, because a number of the items that pass the system areentered into the system several hours before the term for dischargingthe items, e.g. at the make-up operation for a desired flight departure.Therefore, a discharge station must be open for items for a specificdestination for a long period of time before the term for discharge forthat specific destination, thus requiring the system to comprise a highnumber of discharge stations. Furthermore, some items arrive to theconveyor system much earlier than the aforementioned items, oftenreferred to in terms of airport systems as “early bags”, which isbaggage that is checked-in very early or baggage in transit. Mostsystems include an early bag storage unit, such as one or more longconveyors upon which the early bags may be temporarily stored until adischarge station is opened for baggage with the specific destination ofthe early bags.

A high number of discharge stations are costly to install and tomaintain and they take up very large areas because of the arearequirements for providing access for trucks etc. to each dischargestation. Also, the early bag storage units that are formed as longendless conveyors take up plenty of area, for which reason the capacityof those storage units have to be limited.

It is thus an object of the present invention to provide a conveyorsystem with means for reducing the number of discharge stations requiredfor an efficient operation of the system without reducing the sortingcapacity or the conveying capacity of the system.

It is a further object of the invention to provide a storage arrangementthat enables pre-sorting of the stored items according to theirdestination and/or the their term of departure so that items with aspecific destination may be retracted quickly from the storagearrangement and moved to a discharge station dedicated to that specificdestination.

It is a still further object to provide a storage arrangement in whichthe items may be stored in a compact manner so that the arearequirements for the storage arrangement are low.

It is an advantage that the items are placed on trays before they areentered onto the conveyor in order to minimise the risk of damaging theitems when they are conveyed and to prevent that parts of the items,such as e.g. handles or belts, get stuck in the conveyor parts.Furthermore, the trays are more easy to convey and handle by theconveyor systems and especially for a storage arrangement since they areuniform objects in contrast to e.g. baggage.

Thus the present invention relates to a method of conveying items usinga system comprising conveyors and at least one article storagearrangement,

(a) loading items onto trays at at least one loading station of a firstconveyor,

each item being identified and assigned to a destination belonging to agroup of predefined destinations,

 to thereby create articles, each article consisting of a tray carryingat least one item,

(b) conveying articles in the first conveyor, the first conveyor beingcapable of conveying articles from the at least one loading station toan article storage arrangement comprising a plurality of storage unitsin each of which a plurality of articles may be stored,

(c) moving at least some of the articles from the first conveyor intostorage units of the articles storage arrangement,

(d) determining to which set of articles belonging to a predefined groupof sets each of said articles belongs according to the destination ofthe at least one item of the article, at least one of the plurality ofstorage units being assigned to each of said sets,

(e) storing each article in one of the at least one storage unit beingassigned to the set to which the article belongs,

(f) allocating at least one discharge station of a second conveyor,

the second conveyor being adapted to convey articles from the articlestorage arrangement to the at least one discharge station,

 to a destination belonging to the group of predefined destinations,

(g) moving at least some of the articles stored in the article storagearrangement and

being assigned to said destination from the storage units and to thesecond conveyor,

(h) conveying said articles in the second conveyor to said dischargestation, and

(i) discharging the items from the trays of said articles at saiddischarge station.

A plurality of storage units within the storage arrangement makes itpossible to pre-sort the articles when they enters the article storagearrangement. The control means for controlling the operation of theconveyor system may comprise a central control unit that controls alloperations or it may comprise a number of distributed units that eachcontrols a part of the conveyor system, and preferably control meanscomprise a combination of a central control unit and a number ofdistributed units. The control means may further comprise a number ofsensor means, such as photo cells or photosensors, cameras, stresssensitive sensors etc., for detecting the presence of articles atvarious positions on the conveyor system, sensor means for detecting theconveying speed at various positions along the conveyor system, dataentering means for manually entering data into the control system,scanning means for scanning identification marks of items and/or traysconveyed by the system, etc.

It is an advantage for efficient operation of the system thatsubstantially all of the articles are entered into the article storagearrangement in step (c) so that the discharge stations only have to beallocated to receive items for a given destination for a short period ata time, typically a period of the order of 5-15 minutes, because thearticles to be conveyed to the discharge station within the period arepresent in the article storage arrangement. Thus, the discharge stationis only occupied for the short period in which at least a part of theamount of items for a given destination are discharged, and thedischarge station may be allocated to another destination. The dischargestations are utilised very intensively by this method and the number ofdischarge stations for a conveyor system of a given sorting capacitymaybe reduced with 30-80%, depending on the composition of the articleflow through the system.

According to a preferred embodiment of the present invention, at leastsome of the predefined sets of articles solely comprise articles ofwhich the items are assigned to the same destination.

Substantially each of the destinations has a scheduled departure timeassociated with it and an additional or alternative way of defining thesets is that at least some of the predefined sets of articles solelycomprise articles of which the items are assigned to destinations havinga scheduled departure time within a predefined time range. Inparticular, said sets may be defined so that the predefined time rangeof any of said sets does not overlap the predefined time range of any ofthe other of said sets.

The two above described ways of defining sets may be combined so thatarticles assigned to destinations having late departure times arepre-sorted to time-range defined sets which are emptied and pre-sortedto sets defined for given destinations at the time where the latter setsare defined so that the method according to the invention furthercomprises the steps of

(j) assigning at least one of the plurality of storage units to apredefined set of articles solely comprising articles of which the itemsare assigned to a given destination,

(k) moving articles of which the items are assigned to said destinationfrom the at least one storage unit assigned to the set of articles ofwhich the predefined time range includes the departure time of saiddestination to the at least one storage unit having been assigned instep (j).

It is an advantage for the efficiency of the utilisation of thedischarge stations if step (f) is a temporary allocation to adestination during which a subset of a total expected number of itemsbeing assigned to said destination is discharged at said dischargestation, the subset being selected from the items stored in the articlestorage means. Consequently, an operation of discharging the totalnumber of items for a given destination comprises a plurality oftemporary allocations of one or more of the at least one dischargestations.

In order to keep track of which items are present in a given containermeans for containing items, e.g. for security reasons at airports etc.,the whole subset of items may subsequent to the discharging be stored inone container means for containing items. Furthermore, a control meansassociated with the system may be arranged to produce an outputcomprising data that are significant for the identity of each of theitems within the subset of items.

Substantially each of the storage units of the storage arrangement is ina preferred embodiment of the invention designed for permitting aplurality of articles to be disposed aligned in abutting proximity toeach other longitudinally along a generally horizontally elongatedstorage bay, each storage unit comprising a frame defining said storagebay and support means for supporting the articles to be stored in thestorage unit. By designing the storage units in this manner, it isachieved that the articles may be stored very densely, thus taking up aminimal area of space. This is in particular possible because the itemsto be conveyed by the conveyor system are placed in trays.

The support means may e.g. consist of pairs of tracks on which thearticles are resting or the support means may preferably comprisecylindrical rollers or wheels so that the articles may slide into andout from the storage bay with a minimum of friction. The support meansmay comprise conveyor belts or driven cylinders or wheels so that thearticles may be moved within the storage bay, e.g. when they are to beretracted from the storage bay.

The support means of each of the storage units may be arranged slightlydownwardly inclined towards a front end in the longitudinal direction ofthe storage bay of said storage unit so that articles stored in thestorage unit will be drawn towards said front end by the force ofgravity acting on the articles, each of the storage units furthercomprises

movable stopping means that may be positioned so that the stopping meansof said storage unit prevent articles stored in said storage unit frompassing the front end of the storage bay of said storage unit, and

means for moving the stopping means of said storage unit between aposition where the stopping means prevent articles stored in saidstorage unit from passing the front end of the storage bay of saidstorage unit and a position where the stopping means allow articles topass said front end.

In which case the storing of an article in a storage unit according tostep (e) comprises the steps of

(e1) moving the article to the front end of the storage unit,

(e2) in case a previous article already resides in the storage unit,placing the article in abutting contact with the previous article so asto prevent the previous article from passing the front end of thestorage unit when the stopping means are moved to the position where thestopping means allows articles to pass said front end,

(e3) moving the stopping means of the storage unit to the position wherethe stopping means allow articles to pass said front end,

(e4) moving the article into the storage unit by means of pushing meanswhereby the previous article is moved further into the storage unit, and

(e5) moving the stopping means of the storage unit to the position wherethe stopping means prevent articles from passing said front end,

and wherein the removal of an article from a storage unit according tostep (g) comprises the steps of

(g1) engaging the article being in a front end position at the storageunit with withdrawing means so as to prevent the article from passingthe front end of the storage unit when the stopping means are moved tothe position where the stopping means allow articles to pass said frontend,

(g2) moving the stopping means of the storage unit to the position wherethe stopping means allow articles to pass said front end,

(g3) moving the article from the storage unit by means of thewithdrawing means whereby one or more possible further articles presentin the storage unit are moved further towards the front end of thestorage unit, any article being in abutting contact with the articlethat is moved from the storage unit being moved to the front endposition of the storage unit, and

(g4) moving the stopping means of the storage unit to the position wherethe stopping means prevent articles from passing said front end.

Articles may with this particular arrangement be loaded into andretracted from the storage unit from the front end and the storage baysdo not have to be equipped with any active means for driving thearticles or controlling the position of the articles stored within thestorage bay.

In order to enable storage of articles in a dense manner, a plurality ofstorage units may be arranged in a storage rack in at least twovertically spaced generally horizontal levels, said storage units beingarranged so that the longitudinal direction of the storage bays of saidplurality of storage units are substantially parallel and so that thefront ends of the storage bays of said plurality of storage units arearranged in substantially the same vertical plane. By arranging thefront ends of the storage bays in substantially the same vertical plane,it is enabled that articles may be loaded into and retracted from theplurality of storage units by an article handling system that is atleast partly shared by the storage units

In particular, such storage rack may comprise

elevating means for moving articles between the at least two horizontallevels;

shifting means for moving articles in a horizontal level, the shiftingmeans being arranged in a vertical plans substantially parallel to thevertical plane of the front ends of the storage bays of said pluralityof storage units,

first transferring means for transferring articles between the elevatingmeans and the shifting means,

second transferring means for transferring articles between theelevating means and the first and the second conveyor,

loading means comprising pushing means for loading articles from theshifting means into the storage units, and

unloading means comprising withdrawing means for unloading articles fromthe storage units onto the shifting means,

so that step (e) of moving articles from the first conveyor and to eachof the plurality of storage means arranged in the storage rack and step(g) of moving articles from each of the plurality of storage unitsarranged in the storage rack and to the second conveyor may be performedby means of the elevating means, the shifting means, the firsttransferring means, the second transferring means, the loading means andthe unloading means of said storage rack.

The elevating means may in a preferred embodiment comprise two lifts,one lift arranged at one side of the storage rack for loading articlesinto the rack and one lift arranged at the opposite side of the firstlift for retracting articles from the rack. The elevating means arepreferably arranged in substantially the same vertical plane as theshifting means so that articles may easily be transferred between theelevating means and the shifting means.

The system may be operated by means of a central control unit that isenabled to control each step from check-in of an article and until thearticle is discharged from the conveying system, including the positionof each article within the system, or the or the control means maycomprise a number of distributed control units, or the control means maypreferably comprise a combination of distributed control units and oneor more central control units. It is, regardless of the type of controlmeans applied, an advantage for a method according to the presentinvention that each article is labelled with a unique, automaticallyreadable identification mark and the system comprises reading means forreading the identification marks and producing an output accordingly,the reading means being situated at least at one position along the pathof the articles, the method further comprising the steps of

reading the identification marks of substantially each article passingeach of the at least one reading means,

producing an output from the reading means according to each of theidentification mark read, and

communicating said output to the control means of the system.

An identification mark may be placed on the tray, in which case thecontrol means should comprise a central control unit comprising meansfor storing and retrieving data concerning the identity of each of theitems being conveyed by the system and data concerning the identity ofthe tray on which each of said items is placed on. The coupling betweenthe identity data of the item and the identity data of the tray on whichthe item is placed is advantageously established at the loading station.

The identity of an item comprises the destination of the item, whichcomprises the identity of the flight departure in case of an baggagehandling system for an airport. Further, the identity may comprise dataidentifying the owner of the item. The identification mark may be anykind of mark comprising information or data, that are automaticallyreadable, such as e.g. a bar code, a radio transponder that emits aradio signal comprising an identification code upon receiving a requestsignal, visual codes that may be read by one or more optical sensors, acharacter code, that is both automatically readable with an opticalcharacter recognition system and readable by human operators, mechanicalcodes in the form of holes or indentations, a pattern of magneticplates, such as steel plates, that is detectable with inductive sensors,etc.

The advantages of placing an identification mark on the tray are that itenables a nearly completely faultless reading of the identificationmarks, since the trays are largely uniform, at least in one of itsdimensions, and the mark should have substantially the same position onall trays so that the marks can be read by automatic reading means.These reading means may be used for control purposes e.g. to ensure thatthe articles actually are discharged from the conveyor system at thecorrect discharge station, for restarting purposes in situations whereparts of the system have been out of operation for a period, especiallyfor systems with distributed control, in which identification data inthe distributed control units may have been lost, for identificationpurposes to identify an article prior to a handling operation such asX-ray scanning, separation, loading or discharge of an item, etc.

The first and the second conveyor may meet in a separation unit arrangedso that articles are transferred to the separation unit from the firstconveyor and articles may be transferred from the separation unit to thesecond conveyor or to the article storage arrangement, the separationunit comprising means for transferring a given article from theseparation unit to either the second conveyor or the article storagearrangement depending on the identity of the article, said means beingcontrolled by the control means for controlling the operation of theconveyor system.

The method of the present invention is preferably used for operation ofa conveyor system in which the control means of the system comprises anumber of distributed control units. According to such an embodiment,the first and the second conveyors each comprises a plurality ofconveyor sections arranged in series, each given conveyor sectioncomprising a control unit and data communication means, data relating tothe identity of an article that is passing from the preceding conveyorsection to the given conveyor section being communicated from thecontrol unit of the preceding conveyor section to the control unit ofthe given conveyor section by the data communication section of thepreceding conveyor section.

Furthermore, the control means of the system for controlling theoperation of the system and perform the method of the present inventionby means of the system may comprise a central control unit that has datastored regarding the identity of the items placed on each tray, so thatit from the identification of the tray and these data is possible todetermine whether a given tray should be conveyed to one of thedischarge station or should be conveyed to the storage arrangement.Thus, the separation unit may comprise a control unit and datacommunication means, the data communication means be adapted tocommunicate data relating to the identity of an article that is passingfrom the preceding conveyor section to the separation unit from thecontrol unit of the preceding conveyor section to the control unit ofthe separation unit, the data communication means further being adaptedto communicate data relating to the identity of an article that ispassing from the separation unit from the control unit of the separationunit and to either the control unit of the adjacent conveyor section ofthe second conveyor or to a control unit controlling the article storagearrangement, the control unit of the separation unit being adapted tocontrol the means for transferring a given article from the separationunit to either the second conveyor or the article storage arrangement.Additionally, the separation unit may comprise data communication meansfor communication data regarding whether a given article is to betransferred to the article storage arrangement or to the second conveyorfrom the central control unit and to the control unit of the separationunit. The communication between the separation unit and the centralcontrol unit could be arranged so that the central unit by communicationmeans keeps a updated table in the control unit of the separation unitregarding which articles should be conveyed to the discharge stationsand which articles should be conveyed to the storage arrangement, or thecontrol unit of the separation unit could make a request to the centralcontrol unit regarding the direction of each article that arrives at theseparation unit.

The system may furthermore comprise an X-ray unit for X-ray screeningthe items conveyed by the system and a diversion unit for receivingrejected articles, said X-ray unit being arranged so that articles passthe X-ray unit when being conveyed by the first conveyor, the X-ray unitcomprises means for diverting articles to the diversion unit dependingon the result of the screening, the operation of said means and of theX-ray unit being controlled by the control means for controlling theoperation of the conveyor system.

It is also advantageous for the efficiency and flexibility of thepresent method that each of the discharge stations comprises a controlunit for controlling the discharge of articles from the conveyor anddata communication means being adapted to communicate data relating tothe identity of an article passing from the previous conveyor section tothe discharge station from the control unit of the previous conveyorsection and to the control unit of the discharge station, the datacommunicating means further being adapted to communicate data relatingto the identity of an article passing from the discharge station to afollowing conveyor section from the control unit of the dischargestation and to the control unit of the following conveyor section.

The trays that are used with the system are advantageously shaped sothat they have an upper surface of a concave shape as viewed in across-section perpendicular to the longitudinal direction of theconveyors so as to avoid that items carried by the trays may fall offduring transportation. Furthermore, the upper surface of the trays ispreferably coated with a friction increasing material so as to preventitems carried by the trays from falling off during transportation. Asuitable shape as well as surface coating of the trays increase theacceleration that may be applied to the trays in a direction transversalto the conveying direction in order to discharge the trays from theconveyor without causing the items carried on the trays to fall offduring the discharging operation, thus enabling a more efficientdischarge of trays from the conveyor.

Furthermore, the system may comprise a return conveyor for returningempty trays from the at least one discharging station to the at leastone loading station.

The present invention relates also to the conveyor system describedabove by means of which the method of the present invention is carriedout as well as to the storage rack as described.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed.

BRIEF DESCRIPTION OF FIGURES

An embodiment of the present invention is shown in the figures which aregiven by way of illustration only, and thus are not limitative of thepresent invention, and of which

FIG. 1 shows two conveyors each comprising a number of conveyorsections,

FIG. 2 shows a cross-section of a conveyor section,

FIG. 3 shows a loading station for loading items onto trays on theconveyor system,

FIG. 4 shows a discharge station for discharging trays from the conveyorsystem and for discharging items from the trays,

FIG. 5 shows a recycling unit for feeding the empties trays onto aconveyor for conveying the trays to one or more loading stations,

FIG. 6 shows a loading station for loading special trays onto theconveyor system and for loading items onto the special trays,

FIG. 7 shows a discharge station for discharging special trays from theconveyor system and for discharging items from the trays,

FIG. 8 shows a typical correlation between arrival of baggage anddeparture time for the flight at an airport,

FIG. 9 shows an arrangement comprising two linked system of the typeaccording to the invention,

FIG. 10 is a view of a part of a storage rack as seen from the side,

FIG. 11 is a view of a part of a storage rack as seen from above,

FIG. 12 shows a detailed view of a unit for loading trays into andunloading trays from a storage bay of a storage unit in the storage rackand for shifting trays along the front end of a horizontal level of thestorage rack,

FIG. 13 shows one of the lifts used for elevating articles between thedifferent horizontal levels of the storage rack,

FIGS. 14A-H illustrate the procedure of loading an article into astorage bay, and

FIGS. 15A-H illustrate the procedure of unloading an article from astorage bay.

DETAILED DESCRIPTION OF FIGURES

The figures illustrate an embodiment of the system for conveyingarticles according to the invention, wherein the control of the systemis handled by a combination of a central control unit and a number ofdistributed control units, each one being enabled to control theoperation of a section of the system and to communicate data to andother control units of the system.

FIG. 1 shows two conveyors 20, 21 each comprising a number of conveyorsections 22. Each conveyor section has a frame comprising twolongitudinal sidewalls 23, 24 and a number of cross-bars 25 connectingthe two side walls. One of the cross-bars carries an asynchronouselectric motor 26 for driving a roller 27 via a tooth belt transmission.The motor 26 has a built in microprocessor and a frequency converter forregulating the motor 26.

The rollers 27, as shown on FIG. 2, are made from galvanized steeltubes. The rollers 27 are mounted at their end portions withball-bearings on profiles 28 mounted on the side walls 23, 24. Therollers 27 each has a disc 29 mounted near each of their ends fordriving, supporting and centring an endless belt 30 at each side. Thebelts 30 are adapted to convey articles, such as trays 31 which aretransported by the conveyor system.

The belts 30 are further supported by support rollers and supportdevices such as, e.g., tracks, profiles, etc., with low-frictionalsurfaces for minimising friction and thereby wear on the belt and energyconsumption. Aluminium profiles 23′, 24′ mounted along each side wall23, 24 direct and center the trays on the conveyor section.

A photo sensor is mounted near the upstream end of each conveyor sectionfor detecting articles on the conveyor section.

Each conveyor section has its individual control unit for controllingthe conveyor section and for communicating with the control units ofadjacent conveyor sections or other adjacent units, such as loadingstations, discharging stations etc. The control units are standardelectronic units, made, e.g., as hardware units or as programmable unitscomprising a data processing unit and computer readable memory, such as,e.g., EPROM.

In a preferred embodiment of the invention, the operation of a givenconveyor section involves the following steps:

a) in case no article is present on the conveyor section, transmittingdata to the control unit of an immediately preceding conveyor sectionregarding that the given conveyor section is ready to receive anarticle,

b) receiving data from the control unit of the preceding conveyorsection regarding which speed the preceding conveyor section will havewhen an approaching article will pass from the preceding conveyorsection to the given conveyor section,

c) receiving data from the control unit of the preceding conveyorsection regarding the identity of an approaching article,

d) controlling the speed of the given conveyor section so as to obtainsubstantially the same speed as the preceding conveyor when an articleis passing from the preceding conveyor section to the given conveyorsection,

e) passing the article from the preceding conveyor section to the givenconveyor section,

f) detecting that an article has been passed on to the given conveyorsection,

g) receiving data from the control unit of an immediately followingconveyor section regarding that the following conveyor section is readyto receive an article,

h) stopping the conveyor section in case the following section is notready to receive an article,

i) starting the conveyor section if the conveyor section has beenstopped due to data received from the control unit of the followingconveyor section, in case data have been received from the control unitof the following conveyor section regarding that the following sectionis ready to receive an article,

j) selecting at which speed the article should be conveyed whenapproaching the downstream end of the conveyor section, based on apreselected speed for the given individual conveyor section and thepresent speed of the conveyor section,

k) communicating the speed selected in step 1) to the control unit ofthe following conveyor section,

l) transmitting data to the control unit of the following conveyorsection regarding the identity of the article that is approaching thedownstream end of the given conveyor section,

m) varying the speed of the conveyor section so as to reach the speedselected in step j) when the article is approaching the downstream endof the conveyor section,

n) determining the time interval during which the article is beingconveyed by the given conveyor section, based on the signal detected instep f) and on the varying conveying speed,

o) when the article has left the given conveyor section, transmittingdata to the control unit of the preceding conveyor section regardingthat the given conveyor section is ready to receive an article,

p) when an article is no longer present thereon and when no article isapproaching from the preceding conveyor section, stopping the drivemeans of the conveyor section.

The trays 31, 49 on which the items to be transported are placed have aconcave upper surface 32 as when seen in a cross-section perpendicularto the transport direction. Each tray 31, 49 has vertical screens 33provided at the front and rear ends as seen in the transport direction.The concave surface, the screens and the coated with a frictionincreasing material such as natural or synthetic rubber reduce the riskfor items to accidentally leave the tray 31, 49, and at the same timethe concave surface enables discharging of items from the tray 31, 49 bytilting the tray 31, 49. The trays 31, 49 are made of a material whichis preferably both vibration dampening, shock absorbing and knockproof.

The normal trays 31 are of a size that is suitable for containing oneitem of the type that is mostly transported by the conveyor system. Forluggage, a suitable length is between 0.75 m and 1.75 m, preferablyapproximately 1.25 m and a suitable width is between 0.5 m and 1.5 m,preferably approximately 1 m.

As shown on FIG. 3, the trays 31 are loaded with items at one or moreloading stations arranged along the conveyor system. Each loadingstation may comprise one or more loading conveyors 34 which are arrangedwith an acute angle to the conveyor sections so that the items have aspeed in the transport direction of the conveyor sections when beingloaded onto the trays 31, which speed is preferably substantially thesame as the speed of the trays 31 at the loading station. Furthermore,each loading station transmits data regarding the identity of each itemto the control unit of the conveyor section receiving the item. Theconveyor sections at the loading station drive the trays at a handlingspeed between 1 m/s and 2.5 m/s, preferably approximately 1.7 m/s.

An item is discharged from the conveyor system by discharging the traycarrying the item from the conveyor and then discharging the item fromthe tray. A discharge station 35 is shown on FIG. 4, the station 35comprising a discharge surface 36 preferably equipped with roller-ballracks or having another friction reducing design, arranged between twoconveyor sections, a discharge member 37 for discharging trays 31 fromthe discharge surface 36, and an activating device 38 on which themember 37 is mounted, the activating device 38 allowing the member 37 toperform a discharging movement. The station 35 further comprises a firstreceiving surface 39 which is inclined away from the discharge surface36, the receiving surface 39 being adapted for receiving the dischargedtrays 31 from the discharge surface 36 and moving the emptied trays to aconveyor 46. A projecting edge 40 is provided for stopping the movementof the tray 31 along the first receiving surface 39 away from thedischarge surface 36. A second receiving surface 41 for receiving theitem that is discharged from the tray 31 is further comprised in thedischarge station 35. The discharge station 35 further comprises drivemeans for driving the member 37 in its discharging movement and acontrol unit for controlling the discharge of trays 31 from theconveyor.

The device 38 on which the discharge member 37 is mounted comprises twopivots 42, defining two parallel, vertical axes, two first bars 43rigidly connected to the member 37, the spacing between the connectionsof two first bars 43 to the member 37 being substantially the same asthe spacing between the two pivots 42. The device 38 further comprisestwo second bars 44, each of which is pivotally connected to anassociated one of the first bars 43, each second bar 44 further beingconnected to an associated one of said pivots 42.

The device 38 allows the member 37 to perform a discharging movement,during which the member 37 pushes a tray 31 from the discharge surface36 in a direction transverse to the transport direction of the conveyorin order to discharge the tray 31 from the discharge surface 36 onto thefirst receiving surface 39. While the member 37 is in contact with thetray 31, the member 37 is accelerated in the direction transversal tothe longitudinal direction of the conveyor with a substantial constantacceleration of a magnitude so that an item carried on the surface ofthe tray follows the tray during the discharging operation withoutfalling off the tray. Thereby, the tray is discharged fast and thedischarge member 37 is at the same time having a speed in thelongitudinal direction of the conveyor during the discharge operation,whereby the member 37 is prevented from affecting an immediatelyfollowing tray conveyed by the conveyor onto the discharge surface 36.During one discharge movement of the member, the member 37 and thedevice 38 describe one full turn around the pivots 42 so that the member37 returns to its starting position adjacent to the discharge surface 36as illustrated in FIG. 4.

In a preferred embodiment of the invention, the conveyor sectionupstream of the discharge station 35 drives the trays 31 with a handlingspeed which is normally between 1 m/s and 2.5 m/s, preferablyapproximately 1.7 m/s when passing trays 31 to the discharge surface 36.The data identifying the item on an approaching tray 31 are transmittedfrom the control unit of the conveyor section immediately upstream ofthe discharge station 35 to the control unit of the discharge station35. Based on these data, the control unit of the discharge station 35determines whether the tray is to be discharged. In case the tray 31 isto be discharged, the drive means for driving the member 37 areactivated so as to discharge the tray 31. The tray 31 is then slidingdown the first receiving surface 39 which is inclined, until it hits theprojecting edge 40. However, due to gravity and its inertia, the item onthe tray 31 will continue its movement in a direction transverse to thetransport direction of the conveyor, the item thereby being dischargedfrom the tray 31 onto the second receiving surface 41.

In a preferred embodiment, the empty trays 31 are transported from thefirst receiving surface to a recycling unit 45 by a conveyor 46. Therecycling unit 45 which is shown in FIG. 5 comprises a substantiallyhorizontal disc 47 rotating about a substantially vertical axis. Thetrays 31 are loaded onto the disc 47 by the conveyor 46. The trays 31are turned and given a speed in the transport direction of the conveyor21 for conveying the trays to one or more loading stations. The trays 31are fed onto the conveyor 21 by the rotational movement of the disc 47and by an arm 48.

Special trays 49, as shown on FIG. 6, are used for conveying items ofrelatively large dimensions, such as skies, baby carriages etc. Thespecial trays 49 which have a width substantially equal to the width ofthe normal trays 31 have a length normally between 2 m and 8 m,preferably about 5 m.

The special trays 49 are automatically loaded onto the conveyor systemby a roller rack 50 arranged adjacent to the conveyor. The loading ofitems onto the special tray 49 is performed manually at one or morespecial loading stations by placing each item on a chute 51 from whereit slides down to the special tray 49. The loading of the special trays49 onto the conveyor and the loading of items onto the special trays 49is performed when the trays are conveyed at a handling speed normallybetween 1 m/s and 2.5 m/s, preferably approximately 1.7 m/s.

The special trays 49 are discharged from the conveyor system at one ormore special discharge station is 52 as shown on FIG. 7. The dischargedstation 52 comprises activating devices 53 for displacing the specialtrays 49 transversally to the transport direction. The special trays 49are discharged onto a roller rack 54 arranged adjacent to the conveyor.and the items present on the special trays 49 are then dischargedmanually. The discharge of the special trays 49 from the conveyor isnormally performed when the trays are conveyed at a handling speednormally between 1 m/s and 2.5 m/s, preferably approximately 1.7 m/s.

The graph in FIG. 8 shows a typical correlation between arrival ofbaggage and departure time for the flight at an airport, in which thedischarge station, or chute, designated for a specific destination isopened 2 hours 15 minutes before departure of the flight with aconventional baggage conveying system. This period can be subdividedinto an accumulation period of about 1.5 hours duration, wherein lessthan half of the total amount of baggage arrives, and a loading periodof 0.5 hour in which more than half of the baggage arrives and thesorted baggage is transported from the discharge station to thedeparting aircraft.

The opening time for a discharge station in which it is designated toreceive baggage for a specific destination may according to the numberson which FIG. 8 is based be reduced with as much as 75%, which meansthat the number of discharge stations may be reduced with acorresponding part if an efficient storage arrangement is included inthe conveying system so that the discharge stations only need to be openduring the loading period whereas the baggage arriving during theaccumulation period-may be stored in the storage arrangement andconveyed to the discharge station when it is open.

FIG. 9 shows an arrangement comprising two linked system of a typeaccording to the invention, each system comprising twelve check-instations 55 for loading items onto trays 31, reading the identificationmark of the tray 31 and entering the coupling between the identity dataof the item and the identification data of the tray 31 into a centralcontrol unit, an X-ray scanning unit 56 for security scanning of thecontent of the items, a first conveyor 57 for conveying trays 31 fromthe check-in stations 55 to the storage rack 58, conveyors 59 forconveying trays 31 to and from the storage rack 58, a second conveyor 60for conveying trays from the storage rack to the three dischargestations 61 of each system, and a return conveyor 62 for conveying theempty trays 31 back to the check-in stations 55. A second X-ray scanningunit 68 is shown on FIG. 9, to which trays 31 with items that have beenrejected from the first scanning is conveyed for a second scanning inwhich the result of the scanning is checked by a human operator that mayreject the item again or may accept it. The figure also shows connectingconveyors 64 for conveying trays between the two systems in case e.g. anitem that have been checked-in in one of the systems is redirected to adestination to which an discharge station 61 of the other system will bedesignated.

The system shown in FIG. 9 is operated in the following way: A bag ischecked-in at one of the check-in stations 55 at which it is equippedwith an identification tag comprising a automatically readabledestination code in form of a barcode. The item is placed on a tray 31with an identification mark that is read by a scanner, and the datacoupling the identity of the item and the identity of the tray isentered into the memory of a central control unit. The tray 31 with theitem placed upon it is conveyed by the first conveyor 57, that comprisesa number of conveyor sections each equipped with a control unit asdescribed previously and the identity of the item is send from sectionto section along with the tray 31. The tray 31 is conveyed to theseparation unit at which the flow of trays is separated between theconveyors 59 for conveying trays 31 to and from the storage rack 58 andthe second conveyor 60. The separation unit sends a data inquiry to thecentral control unit with the identity of the item when it isapproaching the separation unit. The central control unit replies therequest with a direction to whether the tray with the item upon shouldbe diverted to the storage rack 58 or to the discharge stations 61. Theseparation unit resembles the discharge station as shown in FIG. 4except that the item is not unloaded from the tray 31 in the separationunit. In case the tray 31 is to be stored in the storage rack 58, it ispushed off the separation unit and onto a conveyor 59 that conveys it tothe storage rack 58 and the data identifying the item on the tray 31 iscommunicated from the control unit of the separation unit to the controlunit of the storage rack. The control unit of the storage rack receivesinformation from the central control unit regarding items that have beenchecked-in and for which destinations discharge stations are open andclosed for. The control unit of the storage rack 58 assigns a number ofstorage units to each destination that items are to be pre-sorted andtemporarily stored for and the control unit of the storage rack 58 keepsan updated image of the location of all trays 31 within the storage rack58. When a discharge station 61 is opened for a specific destination thecorresponding storage units of the storage rack 56 are emptied and thetrays 31 carrying the items are entered onto a conveyor 59 and areconveyed to the second conveyor 60 by which they are conveyed to thedischarge station 81 still along with the data identifying each item,which is being communicated from the control unit of one conveyorsection to the control unit of the following. The identity of a tray 31is scanned just before it reaches the discharge stations 61 and theidentity of the tray 31 is together with the identity of the itemcommunicated to the control unit of the discharge station 61 just beforethe tray 31 reaches it. The control unit confirms with the centralcontrol unit that the identities of the tray 31 and the correspondingitem are correct. The tray 31 is discharged from the discharge station61 if the destination of the item corresponds with the destination thedischarge station 61 is opened for. The identity of the tray may bescanned right after the discharge as an alternative to the scanningimmediately before the discharge station 61.

An embodiment of a storage rack 58 is shown in FIGS. 10 and 11 FIG. 10is a view of a part of a storage rack 58 as seen from the side and FIG.11 is a view as seen from above. Each storage unit of the rack 58comprises a storage bay 65 defined by the frame part 66 of the rack 58,a number of steel rollers 67 on which the trays 31 may slide, arrangedinclining towards a front end 68 of the storage bay 65. Each storageunit further comprises a loading unit 69 for loading trays 31 into andunloading trays 31 from the storage bay 65 of the storage unit in thestorage rack 58 and for shifting trays 31 along the front end of ahorizontal level of the storage rack 58. Details of such a loading unit69 are shown in FIG. 12.

The trays 31 are moved between the horizontal levels by two lifts 70,one lift 70 arranged at one side of the storage rack 58 for loadingtrays 31 into the track 58 and one lift 70 arranged at the opposite sideof the first lift 70 for unloading trays 31 from the rack 58. The lifts70 are placed in substantially the same vertical plane as the loadingunits 69 so that trays 31 easily may be transferred between the lifts 70and the loading units 69. Details of a lift 70 are shown in FIG. 13.

FIG. 12 shows a detailed view of a loading unit 69 for loading trays 31into and unloading trays 31 from a storage bay 65 of a storage unit inthe storage rack 58 and for shifting trays 31 along a horizontal levelof the front end of the storage rack 58. The operation of the loadingunit 69 is illustrated in FIGS. 14A-H and FIGS. 15A-H. The loading unit69 comprises a frame part 71 of which a front end 72 is arranged on theframe part 66 of the storage rack 58, so that the front end of the framepart 71 is adjacent to the lower side of the front end 68 of a storagebay 65. On the frame part 71 is mounted shifting means for shiftingtrays 31 along the front end of a horizontal level of the storage rack58, the shifting means comprising two conveyor belts 73 (only one isshown on FIG. 12) and an asynchronous electro motor 74 for driving thebelts 73. A bracket 75 equipped with a row of wheels 76 on each side isused to give the trays 31 the correct position and inclination, which isfour degrees to horizontal, equivalent to the inclination of the steelrollers 67. The bracket 75 is hinged to the frame part 71 and theinclination is established when the front end of the bracket 75 islifted by lifting means (not shown) and a tray 31 that is placed in theloading unit 69 will at the same time be lifted from the belts 73 by thebracket 75. Stopping means 77 arranged at the front end 72 of the framepart 71 also constitute part of the loading unit 69. The stopping means77 may be moved between two positions, one in which they prevent trays31 stored in the adjacent storage bay 65 from sliding out from thestorage bay 65 and one position for allowing trays 31 to be loaded intoand unloaded from the storage bay 65. A pushing member 78 is arranged onthe bracket 75 for pushing trays 31 into the storage bay 65 and forsupporting trays when they are unloaded from the storage bay 65. Themovement of the pushing member 78 is driven by an asynchronous electromotor 79. The loading unit 69 comprises for control means two photosensors for detecting the presence and position of trays 31 on theloading unit at two positions perpendicular to the conveying directionof the conveyor belts 73. The photo sensors are arranged so that a trayentering the loading unit 69 has a correct position for being loadedinto the storage bay 65 when the first photo sensor has been blocked andagain is unblocked and the second photo sensor is still unblocked.

FIG. 13 shows one of the lifts 70 used for elevating trays 31 betweenthe different horizontal levels of the storage rack 58. The lift 70comprises a car 80 equipped with two longitudinal side walls 81 and twoconveyor belts 82 for conveying trays 31 placed in the car 80 in adirection parallel to the front end of the storage rack 58 and the lift70 is arranged so that the car is placed in the same vertical plans asthe loading units 69 of the storage rack 58. The conveyor belts 82 aredriven by an asynchronous electro motor 83. The lift 70 also comprises asubstantially vertical stake 64 to which the car 80 is slidablyconnected so that the car 80 may slide up and down. The verticalmovement of the car 80 is driven by an asynchronous electro motor 85.

FIGS. 14A-H illustrate the procedure of loading a tray 86 into a storagebay 65. The procedure comprises the steps of:

FIG. 14A: The new tray 86 to be loaded into the storage bay 65 whereanother tray 87 is already stored, is entered onto the loading unit 69by means of the conveyor belts 73 and is positioned correctly by meansof the photo sensors. The tray 87 present in the storage bay 65 isprevented from sliding out from the storage bay 65 by the stopping means77.

FIG. 14B: The bracket 75 is lifted by the lifting means so that it is inline with the support means of the storage unit and inclined fourdegrees to horizontal.

FIG. 14C: The pushing member 78 is activated so that the tray 87resident in the storage bay 65 is pushed out of contact with thestopping means 77 so that they can be pulled down and allow the tray 86to enter the storage bay 65. The trays 31 used with the system aredesigned so that they when being in abutting contact have enough spacein between at the positions of the stopping means so that the stoppingmeans may slide up and down.

FIG. 14D: The stopping means 77 have been pulled down and the pushingmember 78 moves the tray 86 into the storage bay 65.

FIG. 14E: The stopping means 77 are pushed up in the stopping positionso as to prevent the tray 86 from sliding out from the storage bay 65.

FIG. 14F: The pushing member 78 is slowly retracted so that the tray 86comes into contact with the stopping means 77.

FIG. 14G: The pushing member 78 is returned to its initial position .

FIG. 14H: The bracket 75 is returned to a substantially horizontalposition and the loading unit 69 is ready to start a new operation.

FIGS. 15A-H illustrate the procedure of unloading a tray 88 from astorage bay 65. The procedure comprises the steps of:

FIG. 15A: The bracket 75 is lifted by the lifting means so that it is inline with the support means of the storage unit and inclined fourdegrees to horizontal.

FIG. 15B: The pushing member 78 is moved towards the storage bay 65 sothat the tray 88 is pushed out of contact with the stopping means 77.

FIG. 15C: The stopping means 77 are pulled down so as to allow the tray88 to leave the storage bay 65.

FIG. 15D: The pushing member 78 is moved back so that the tray 88 ismoved onto the loading unit 69. The pushing member 78 stops at aposition that allows for the stopping means 77 to be pushed up so as toprevent the following tray 89 in the storage bay 65 from sliding outfrom the storage bay 65.

FIG. 15E: The pushing member 78 is slowly retracted so that the tray 89comes into contact with the stopping means 77.

FIG. 15F: The pushing member 78 is returned to its initial position andthe tray 88 moves with it and onto the loading unit 69.

FIG. 15G: The bracket 75 is returned to a substantially horizontalposition and the tray 88 comes into contact with the conveyor belts 73.

FIG. 15H: The tray 88 is conveyed by the conveyor belts 73 towards alift 70 and the loading unit 69 is ready to start a new operation.

The invention being thus described, it will be obvious that the same bybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodification as would be obvious to be one skilled n the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A method of conveying items using a systemcomprising conveyors and at least one article storage arrangement, themethod comprising the steps of: (a) loading items onto trays at leastone loading station of a first conveyor, each item being identified andassigned to a destination belonging to a group of predefineddestinations, to thereby create articles, each article includes a traycarrying at least one item, (b) conveying articles in the firstconveyor, the first conveyor being capable of conveying articles fromthe at least one loading station to an article storage arrangementcomprising a plurality of storage units in each of which a plurality ofarticles may be stored, (c) moving substantially all of the articlesfrom the first conveyor into storage units of the articles storagearrangement, (d) determining to which set of articles belong to apredefined group of sets each of said articles belongs according to thedestination of the at least one item of the article, at least one of theplurality of storage units being assigned to each of said sets, (e)storing each article in one of the at least one storage unit beingassigned to the set to which the article belongs, (f) allocating atleast one discharge station of a second conveyor, the second conveyorbeing adapted to convey articles from the article storage arrangement tothe at least one discharge station, to a destination belonging to thegroup of predefined destinations, (g) moving at least some of thearticles stored in the article storage arrangement and being assigned tosaid destination from the storage units and to the second conveyor, (h)conveying said articles in the second conveyor to said dischargestation, and (i) discharging the items from the trays of said articlesat said discharge station.
 2. A method according to claim 1, wherein atleast some of the predefined sets of articles solely comprise articlesof which the items are assigned to the same destination.
 3. A methodaccording to claim 1, wherein substantially each of the destinations hasa scheduled departure time associated with it and at least some of thepredefined sets of articles solely comprise articles of which the itemsare assigned to destinations having a scheduled departure time within apredefined time range.
 4. A method according to claim 3, wherein thepredefined time range of any of said sets does not overlap thepredefined time range of any of the other of said sets.
 5. A methodaccording to claim 3 further comprising the steps of (j) assigning atleast one of the plurality of storage units to a predefined set ofarticles solely comprising articles of which the items are assigned to agiven destination, (k) moving articles of which the items are assignedto said destination from the at least one storage unit assigned to theset of articles of which the predefined time range includes thedeparture time of said destination to the at least one storage unithaving been assigned in step (j).
 6. A method according to claim 1,wherein the step (f) is a temporary allocation to a destination duringwhich a subset of a total expected number of items being assigned tosaid destination is discharged at said discharge station, the subsetbeing selected from the items stored in the article storage means.
 7. Amethod according to claim 6, wherein an operation of discharging thetotal number of items for a given destination comprises a plurality oftemporary allocations of one or more of the at least one dischargestations.
 8. A method according to claim 6, wherein, subsequent to thedischarging, the whole subset of items is stored in one container meansfor containing items.
 9. A method according to claim 8, wherein acontrol means associated with the system produces an output comprisingdata that are significant for the identity of each of the items withinthe subset of items.
 10. A method according to claim 1, whereinsubstantially each of the storage units of the storage arrangement isdesigned for permitting a plurality of articles to be disposed alignedin abutting proximity to each other longitudinally along a generallyhorizontally elongated storage bay, each storage unit comprising a framedefining said storage bay and support means for supporting the articlesto be stored in the storage unit.
 11. A method according to claim 10,wherein the support means of each of the storage units are arrangedslightly downwardly inclined towards a front end in the longitudinaldirection of the storage bay of said storage unit so that articlesstored in the storage unit will be drawn towards said front end by theforce of gravity acting on the articles, each of the storage unitsfurther comprises movable stopping means that may be positioned so thatthe stopping means of said storage unit prevent articles stored in saidstorage unit from passing the front end of the storage bay of saidstorage unit, and means for moving the stopping means of said storageunit between a position where the stopping means prevent articles storedin said storage unit from passing the front end of the storage bay ofsaid storage unit and a position where the stopping means allow articlesto pass said front end, wherein the storing of an article in a storageunit according to step (e) comprises the steps of (e1) moving thearticle to the front end of the storage unit, (e2) in case a previousarticle already resides in the storage unit, placing the article inabutting contact with the previous article so as to prevent the previousarticle from passing the front end of the storage unit when the stoppingmeans are moved to the position where the stopping means allows articlesto pass said front end, (e3) moving the stopping means of the storageunit to the position where the stopping means allow articles to passsaid front end, (e4) moving the article into the storage unit by meansof pushing means whereby the previous article is moved further into thestorage unit, and (e5) moving the stopping means of the storage unit tothe position where the stopping means prevent articles from passing saidfront end, and wherein the removal of an article from a storage unitaccording to step (g) comprises the steps of (g1) engaging the articlebeing in a front end position at the storage unit with withdrawing meansso as to prevent the article from passing the front end of the storageunit when the stopping means are moved to the position where thestopping means allow articles to pass said front end, (g2) moving thestopping means of the storage unit to the position where the stoppingmeans allow articles to pass said front end, (g3) moving the articlefrom the storage unit by means of the withdrawing means whereby one ormore possible further articles present in the storage unit are movedfurther towards the front end of the storage unit, any article being inabutting contact with the article that is moved from the storage unitbeing moved to the front end position of the storage unit, and (g4)moving the stopping means of the storage unit to the position where thestopping means prevent articles from passing said front end.
 12. Amethod according to claim 10, wherein a plurality of storage units arearranged in a storage rack in at least two vertically spaced generallyhorizontal levels, said storage units being arranged so that thelongitudinal direction of the storage bays of said plurality of storageunits are substantially parallel and so that the front ends of thestorage bays of said plurality of storage units are arranged insubstantially the same vertical plane.
 13. A method according to claim12, wherein the storage rack comprises elevating means for movingarticles between the at least two horizontal levels, shifting means formoving articles in a horizontal level, the shifting means being arrangedin a vertical plane substantially parallel to the vertical plane of thefront ends of the storage bays of said plurality of storage units, firsttransferring means for transferring articles between the elevating meansand the shifting means, second transferring means for transferringarticles between the elevating means and the first and the secondconveyor, loading means comprising pushing means for loading articlesfrom the shifting means into the storage units, and unloading meanscomprising withdrawing means for unloading articles from the storageunits onto the shifting means, so that step (e) of moving articles fromthe first conveyor and to each of the plurality of storage meansarranged in the storage rack and step (g) of moving articles from eachof the plurality of storage units arranged in the storage rack and tothe second conveyor may be performed by means of the elevating means,the shifting means, the first transferring means, the secondtransferring means, the loading means and the unloading means of saidstorage rack.
 14. A method according to claim 1, wherein each article islabelled with a unique, automatically readable identification mark andthe system comprises reading means for reading the identification marksand producing an output accordingly, the reading means being situated atleast at one position along the path of the articles, the method furthercomprising the steps of reading the identification marks ofsubstantially each article passing each of the at least one readingmeans, producing an output from the reading means according to each ofthe identification mark read, and communicating said output to thecontrol means of the system.
 15. A method according to claim 14, whereinan identification mark is placed on the tray, and the control meanscomprises a central control unit comprising means for storing andretrieving data concerning the identity of each of the items beingconveyed by the system and data concerning the identity of the tray onwhich each of said items is placed on.
 16. A method according to claim1, wherein the system comprises a separation unit arranged so thatarticles are transferred to the separation unit from the first conveyorand articles may be transferred from the separation unit to the secondconveyor or to the article storage arrangement, the separation unitcomprising means for transferring a given article from the separationunit to either the second conveyor or the article storage arrangementdepending on the identity of the article, said means being controlled bythe control means for controlling the operation of the conveyor system.17. A method according to claim 1, wherein the first and the secondconveyors each comprises a plurality of conveyor sections arranged inseries, each given conveyor section comprising a control unit and datacommunication means, data relating to the identity of an article that ispassing from the preceding conveyor section to the given conveyorsection being communicated from the control unit of the precedingconveyor section to the control unit of the given conveyor section bythe data communication section of the preceding conveyor section.
 18. Amethod according to claim 17, wherein the separation unit comprises acontrol unit and data communication means, the data communication meansbeing adapted to communicate data relating to the identity of an articlethat is passing from the preceding conveyor section to the separationunit from the control unit of the preceding conveyor section to thecontrol unit of the separation unit, the data communication meansfurther being adapted to communicate data relating to the identity of anarticle that is passing from the separation unit from the control unitof the separation unit and to either the control unit of the adjacentconveyor section of the second conveyor or to a control unit controllingthe article storage arrangement, the control unit of the separation unitbeing adapted to control the means for transferring a given article fromthe separation unit to either the second conveyor or the article storagearrangement.
 19. A method according to claim 18, wherein the separationunit comprises data communication means for communication data regardingwhether a given article is to be transferred to the article storagearrangement or to the second conveyor from the central control unit andto the control unit of the separation unit.
 20. A method according toclaim 17, wherein each of the discharge stations comprises a controlunit for controlling the discharge of articles from the conveyor anddata communication means being adapted to communicate data relating tothe identity of an article passing from the previous conveyor section tothe discharge station from the control unit of the previous conveyorsection and to the control unit of the discharge station, the datacommunicating means further being adapted to communicate data relatingto the identity of an article passing from the discharge station to afollowing conveyor section from the control unit of the dischargestation and to the control unit of the following conveyor section.
 21. Amethod according to claim 1, wherein the system comprises an X-ray unitfor X-ray screening the items conveyed by the system and a diversionunit for receiving rejected articles, said X-ray unit being arranged sothat articles pass the X-ray unit when being conveyed by the firstconveyor, the X-ray unit comprises means for diverting articles to thediversion unit depending on the result of the screening, the operationof said means and of the X-ray unit being controlled by the controlmeans for controlling the operation of the conveyor system.
 22. A methodaccording to claim 1, wherein the trays have an upper surface of aconcave shape as viewed in a cross-section perpendicular to thelongitudinal direction of the conveyors.
 23. A method according to claim1, wherein the upper surface of the trays is coated with a frictionincreasing material.
 24. A method according to claim 1, wherein thesystem comprises a return conveyor for returning empty trays from the atleast one discharge station to the at least one loading station.
 25. Asystem for conveying items comprising at least one loading station forloading items onto trays, at least one discharge station for dischargingitems from the trays, a first conveyor and a second conveyor forconveying articles, each article comprising a tray carrying at least oneitem, said first conveyor being arranged for conveying articles from theat least one loading station and to an article storage arrangement andsaid second conveyor being arranged for conveying articles from thearticle storage arrangement and to the at least one discharge station,an article storage arrangement comprising a plurality of storage unitsin each of which a plurality of articles may be stored, means for movingarticles from the first conveyor and to each of the plurality of storageunits, and means for moving articles from each of the plurality ofstorage units and to the second conveyor, and control means forcontrolling the operation of the conveyor system according to the methodclaim
 1. 26. A system according to claim 25, wherein substantially eachof the storage units of the storage arrangement is designed forpermitting a plurality of articles to be disposed aligned in abuttingproximity to each other longitudinally along a generally horizontallyelongated storage bay, each storage unit comprising a frame definingsaid storage bay and support means for supporting the articles to bestored in the storage unit.
 27. A system according to claim 26, whereinthe support means of each of the storage units are arranged slightlydownwardly inclined towards a front end in the longitudinal direction ofthe storage bay of said storage unit so that articles stored in thestorage unit will be drawn towards said front end by the force ofgravity acting on the articles, each of the storage units furthercomprises movable stopping means that may be positioned so that thestopping means of said storage unit prevents articles stored in saidstorage unit from passing the front end of the storage bay of saidstorage unit, and means for moving the stopping means of said storageunit between a position where the stopping means prevents articlesstored in said storage unit from passing the front end of the storagebay of said storage unit and a position where the stopping means allowsarticles to pass said front end.
 28. A system according to claim 26,wherein a plurality of storage units are arranged in a storage rack inat least two vertically spaced generally horizontal levels, said storageunits being arranged so that the longitudinal direction of the storagebays of said plurality of storage units are substantially parallel andso that the front ends of the storage bays of said plurality of storageunits are arranged in substantially the same vertical plane.
 29. Asystem according to claim 28, wherein the storage rack compriseselevating means for moving articles between the at least two horizontallevels, shifting means for moving articles in a horizontal level, theshifting means being arranged in a vertical plane substantially parallelto the vertical plane of the front ends of the storage bays of saidplurality of storage units, first transferring means for transferringarticles between the elevating means and the shifting means, secondtransferring means for transferring articles between the elevating meansand the first and the second conveyor, loading means for loadingarticles from the shifting means into the storage units, and unloadingmeans for unloading articles from the storage units onto the shiftingmeans, so that articles may be moved from the first conveyor and to eachof the plurality of storage means arranged in the storage rack articlesmay be moved from each of the plurality of storage units arranged in thestorage rack and to the second conveyor by means of the elevating means,the shifting means, the first transferring means, the secondtransferring means, the loading means and the unloading means of saidstorage rack.
 30. A system according to claim 25, wherein each articleis labelled with a unique, automatically readable identification markand the system comprises reading means for reading the identificationmarks and producing an output accordingly, the reading means beingsituated at least at one position along the path of the articles.
 31. Asystem according to claim 30, wherein an identification mark is placedon the tray and the control means comprises a central control unitcomprising means for storing and retrieving data concerning the identityof each of the items being conveyed by the system and data concerningthe identity of the tray on which each of said items is placed.
 32. Asystem according to claim 25, comprising a separation unit arranged sothat articles are transferred to the separation unit from the firstconveyor and articles may be transferred from the separation unit to thesecond conveyor or to the article storage arrangement, the separationunit comprising means for transferring a given article from theseparation unit to either the second conveyor or the article storagearrangement depending on the identity of the article, said means beingcontrolled by the control means for controlling the operation of theconveyor system.
 33. A system according to claim 25, wherein the firstand the second conveyors each comprises a plurality of conveyor sectionsarranged in series, each given conveyor section comprising a controlunit and data communication means, data relating to the identity of anarticle that is passing from the preceding conveyor section beingcommunicated to the given conveyor section from the control unit of thepreceding conveyor section to the control unit of the given conveyorsection by means of the data communication means of the precedingconveyor section.
 34. A system according to claim 33, wherein theseparation unit comprises a control unit and data communication means,the data communication means being adapted to communicate data relatingto the identity of an article that is passing from the precedingconveyor section to the separation unit from the control unit of thepreceding conveyor section to the control unit of the separation unit,the data communication means further being adapted to communicate datarelating to the identity of an article that is passing from theseparation unit from the control unit of the separation unit and toeither the control unit of the adjacent conveyor section of the secondconveyor or to a control unit controlling the article storagearrangement, the control unit of the separation unit being adapted tocontrol the means for transferring a given article from the separationunit to either the second conveyor or the article storage arrangement.35. A system according to claim 34, wherein the separation unitcomprises data communication means for communication data regardingwhether a given article is to be transferred to the article storagearrangement or to the second conveyor from the central control unit andto the control unit of the separation unit.
 36. A system according toclaim 25, comprising an X-ray unit for X-ray screening the itemsconveyed by the system and a diversion unit for receiving rejectedarticles, said X-ray unit being arranged so that articles pass the X-rayunit when being conveyed by the first conveyor, the X-ray unit comprisesmeans for diverting articles to the diversion unit depending on theresult of the screening, the operation of said means and of the X-rayunit being controlled by the control means for controlling the operationof the conveyor system.
 37. A system according to claim 25, wherein eachof the discharge stations comprises a control unit for controlling thedischarge of articles from the conveyor and data communication meansbeing adapted to communicate data relating to the identity of an articlepassing from the previous conveyor section to the discharge station fromthe control unit of the previous conveyor section and to the controlunit of the discharge station, the data communicating means furtherbeing adapted to communicate data relating to the identity of an articlepassing from the discharge station to a following conveyor section fromthe control unit of the discharge station and to the control unit of thefollowing conveyor section.
 38. A system according to claim 25, whereinthe trays have an upper surface of a concave shape as viewed in across-section perpendicular to the longitudinal direction of theconveyors.
 39. A system according to claim 25, wherein the upper surfaceof the trays is coated with a friction increasing material.
 40. A systemaccording to claim 25, and comprising a return conveyor for returningempty trays from the at least one discharge station to the at least oneloading station.